I. Field of the Invention
The present invention relates generally to rotary sensors.
II. Description of Related Art
In automotive vehicles, the throttle pedal has traditionally been mechanically connected to the engine throttle by a cable. In more modern vehicles, however, a throttle position sensor is mechanically connected to the pedal and generates an electrical signal indicative of the degree of depression of the throttle pedal. Such systems are sometimes termed “fly by wire” systems.
In one type of previously known throttle position sensor, the sensor includes a transmitter or exciter coil that is excited by a high frequency source and generates electromagnetic radiation at the frequency of the high frequency source. This transmitter coil, furthermore, is typically arranged in a circular pattern although other pattern configurations may alternatively be used.
A receiver coil is also disposed in the throttle position sensor adjacent the transmitter coil. Consequently, the receiver coil generates a receiver signal when the transmitter coil is excited due to inductive coupling between the receiver and the transmitter coil.
Unlike the transmitter coil, however, the receiver coil includes at least a first and second loop that are oppositely wound with respect to each other when viewed in plan. Consequently, the inductive coupling between the transmitter coil and the first loop of the receiver coil generates a voltage opposite in polarity from the inductive coupling between the transmitter coil and the second loop of the receiver coil. The loops of the receiver coil are connected in series so that the receiver output signal is a combination or sum of the signals from the first and second loops of the receiver coil.
In order to generate an output signal representative of the position of the throttle, a coupler element is rotatably mounted within the throttle position sensor so that the coupler element rotates in synchronism with the depression and release of the throttle pedal. This coupler element, furthermore, overlies a portion of both the transmitter and the receiver coils. The coupler element is constructed of a conductive material which cancels magnetic flux through the generation of eddy currents within the coupler element. Consequently, upon rotation of the coupler, the inductive coupling between the transmitter and the first and second loops of the receiver coil are varied thus producing a voltage output from the overall receiver coil indicative of the angular position of the coupler, and thus the position of the throttle pedal.
Assuming that the coupling element is precisely concentric with the transmitter and receiver coil, and that the space in between the coupler element and the transmitter and receiver coils remains constant during the entire movement of the coupler element, the output from the receiver coil provides a precise indication of the angular position of the coupler element, and thus of the position of the throttle pedal. In practice, however, manufacturing tolerances during the manufacture of the throttle position sensor oftentimes produce a throttle position sensor in which the coupler element is not precisely concentric with the transmitter and receiver coils and/or the coupler element does not maintain an even spacing between the coupler element and the transmitter and receiver coils during the entire pivotal or rotational movement of the coupler element. Any lack of concentricity of the coupler element with the transmitter and receiver coils, as well as a variation in the space in between the coupler element and the receiver coils during rotation or pivoting of the coupler element, will vary the inductive coupling between the transmitter coil and the first and second loops of the receiver coil which, in turn, provides an output signal from the receiver coil which varies from the throttle position sensor with a precisely positioned coupler element at the same angular position.